Transfer tanks come in a few standard profiles, and the choice is really a question about your bed rather than about fuel. Each shape trades capacity against the floor space it leaves behind.
Which Shape Should You Choose?
L shape for the most capacity, rectangle for the simplest install, column when floor space matters most. An L shape wraps over the wheel wells and down onto the floor. A rectangle sits straight across the front of the bed. A column stands tall and narrow against the bulkhead.
L Shape Tanks
The L profile uses the space above the wheel wells that nothing else can use, which is why it gives the highest capacity for a given bed length. Tanks in the 90 to 110 gallon range are common in this shape.
The cost is that the tank spreads across more of the floor. It also puts a good deal of weight fairly high, so check the payload figure carefully before choosing the largest option available.
Rectangle Tanks
A rectangle is the straightforward choice. It sits across the front of the bed, it is the easiest to strap or bolt down and its flat sides make it simple to brace against the bulkhead.
- Simplest to mount and to secure properly.
- Leaves a clean rectangular floor area behind it.
- Pairs neatly with a crossover box above or behind it.
- Commonly offered from around 50 gallons up to 100 gallons.
Column Tanks
A column tank is tall and narrow, standing against the bulkhead. It gives up capacity to keep the bed floor as clear as possible, which is the right trade on a truck that carries material as well as fuel.
It is also the easiest shape to work around, since the fill point and the pump end up at a comfortable height rather than at your feet. Capacities are smaller for the same footprint, so expect to trade range for floor.
Combos Are a Fourth Option
A combo unit puts a tool box on top of the tank and uses one footprint for both. On a truck that needs fuel and secure storage anyway, that is usually cheaper than buying the two separately and it stops them competing for the front of the bed.
Weight Applies to All Three
Diesel weighs roughly 7 lb per gallon, so 100 gallons is about 700 lb of fuel before the tank is counted. Whatever shape you choose, that load has to be bolted down rather than strapped, and it has to fit inside the truck's payload alongside the crew and everything else in the bed.
Compare capacities and profiles in transfer tanks, and see truck tool boxes if fuel gear needs somewhere secure to live.